Bisphenols are useful chemical intermediates for the preparation of polymers, for example epoxy resins, polycarbonates, and bifunctional poly(phenylene ether)s. Of particular interest are bisphenols in which the two monohydric phenol groups are linked by an aliphatic carbon atom. The divalent linking group for two monohydric phenols can be, for example, methylene (as in bisphenol F), ethylidene (as in bisphenol E), or 2,2-propylidene (as in bisphenol A).
Bisphenols can be made by reaction of a carbonyl compound with two or more equivalents of a monohydric phenol using an acid or base catalyst. Mineral acid catalysts, for example hydrochloric acid or sulfuric acid, can be used. However corrosion of metal reactors and fittings can be a major problem when hydrochloric acid is used. Moreover, the yield of bisphenol obtained using hydrochloric acid can be low. With sulfuric acid, sulfonated impurities can be formed as byproducts, which reduces the yield and purity of bisphenol. The bisphenols so made may not be suitable as intermediates without purification to remove sulfonated byproducts. Acid-functional ion exchange resins can also be used. However there is room for improvement in the yield and purity of the bisphenols produced using acid-functional ion exchange resins as well. An improved method for manufacture of bisphenols, which does not suffer from the drawbacks associated with the use of mineral acid catalysts or acid-functional organic ion exchange resins, and which produces bisphenols in higher yield and purity, and at a lower cost, is desirable.